In photolithography techniques, for example, there can be performed the steps of forming a resist film made of a resist composition on a substrate, selectively exposing the resist film to radiation such as light or electron beam through a photomask having a predetermined pattern formed thereon, and subjecting to a development treatment to form a resist pattern having a predetermined shape on the resist film. Using this resist pattern as a mask, an insulation film and a conductive film formed on the substrate are partially etched and also the unnecessary resist pattern is removed, and thus transfer of the pattern onto the substrate is completed.
A resist composition in which the exposed area shifts to be soluble in a developer is referred to as a positive resist composition, whereas, a resist composition in which the exposed area shifts to be insoluble in a developer is referred to as a negative resist composition.
In recent years, advances in lithography techniques have led to rapid miniaturization of resist patterns in the production of semiconductor devices and liquid crystal display devices. As means for miniaturization, further progress has been made in shortening of the wavelength of exposure light. Although ultraviolet ray typified by g-ray or i-ray has conventionally been used, KrF excimer laser (248 nm) is introduced at present and also ArF excimer laser (193 nm) is introduced.
To reproduce a pattern having a fine size, a resist material having high resolution is required.
As such a resist material, a chemically amplified resist composition containing a base resin and an acid generator which generates an acid under exposure is used. For example, a positive chemically amplified photoresist contains a resin component which exhibits increased alkali solubility under the action of an acid, and an acid generator component which generates an acid under exposure, and when the acid is generated from the acid generator under exposure during the formation of a resist pattern, the exposed area shifts to an alkali soluble state.
As the resin component of the chemically amplified positive resist composition, there can be commonly used a resin in which a portion of hydroxyl groups of a polyhydroxystyrene-based resin are protected with acid dissociable, dissolution inhibiting groups, and a resin in which a portion of carboxy groups of an acryl-based resin are protected with acid dissociable, dissolution inhibiting groups. As the acid dissociable, dissolution inhibiting groups, there can be used a so-called acetal group, for example, a chain ether group typified by a 1-ethoxyethyl group and a cyclic ether group typified by a tetrahydropyranyl group; a tertiary alkyl group typified by a tert-butyl group; and a tertiary alkoxycarbonyl group typified by a tert-butoxycarbonyl group (see, for example, Patent Reference 1).
However, since a conventional resist composition is insufficient in dry etching resistance, there arises a problem that a resist pattern disappears during etching and etching cannot be performed with high accuracy, resulting in defects of the resist pattern.
Patent Reference 2 (Japanese Unexamined Patent Application, First Publication No. Hei 10-282649) discloses, as means for improving etching resistance of a resist composition, that fullerene is mixed with a resist composition, and a resist pattern is formed using the mixture. Fullerene has properties capable of improving etching resistance.
(Patent Reference 1)    Japanese Unexamined Patent Application, First Publication No. 2002-341538
(Patent Reference 2)    Japanese Unexamined Patent Application, First Publication No. Hei 10-282649
However, according to the prior art, it is difficult to meet both of a demand of forming a fine and high-accuracy resist pattern and a demand of obtaining a resist pattern having high etching resistance. Particularly in a positive resist composition, this problem becomes severe.
The reason is as follows. That is, when a component having etching resistance is combined or mixed during the synthesis of materials of a resist composition or the preparation of the resist composition, it is difficult to form a fine and high-accuracy resist pattern.
For example, a substance having a conjugated double bond such as benzene ring contributes to an improvement in etching resistance. However, since the substance scarcely transmits far-ultraviolet ray having a wavelength of 193 nm, it becomes difficult to perform exposure when the substance is mixed with a resist composition.
Also, a substance having a cyclic structure of carbon atoms has properties capable of improving etching resistance. However, such a substance has low solubility in a developer and can deteriorate developability.
As described above, since it is required to use an exposure light source having a short wave length and to prevent development residue so as to obtain a fine resist pattern, any substance having properties capable of improving etching resistance cannot be mixed with the resist composition. Therefore, a material which enables to form a pattern having a width of 100 nm or less and has high etching resistance has not been found yet.
The present invention has been made so as to solve the above problem and an object thereof is to provide a fine resist pattern which has high accuracy and is excellent in etching resistance.